Question

6. A sample of nitrogen gas weighs 130 g. Write the chemical formula for nitrogen gas. Howmany molecules of elemental nitrogen is this? How many atoms of nitrogen are in this sample?

Answer 1

Chemical formula for nitrogen gas is N₂.

To find the number of molecules in the given sample, we have to convert the mass of the sample to moles by using the molecular mass of elemental nitrogen (N₂).

$130gN_2\cdot\frac{1molN_2}{28gN_2}=4.64molN_2$

Now, we have to use Avogadro's number (6.022x10^23) that indicates the number of molecules in one mole of substance:

$4.64molN_2\cdot\frac{6.022\times10^{23}molecules}{1molN_2}=2.79\times10^{24}molecules$

It means that there are 2.79x10^24 molecules of elemental nitrogen.

To find the number of atoms we just have to multiply the number of molecules by 2, which is the number of atoms of nitrogen per molecule of elemental nitrogen:

$2.79\times10^{24}molecules\cdot\frac{2atoms}{1molecule}=5.59\times10^{24}atoms$

There are 5.59x10^24 atoms of nitrogen in the sample.